by

I too think these are Tsessebe (also called Topi), Damaliscus lunatus. Not only do the horns match the tsessebe rather than the red hartebeest, but the hind quarters are not the white of the hartebeest. Also the tail of the tsessbe is pale like these here, while the tail of the hartebeest is dark. And to top it off, these had the pronounced hump at the shoulders like tsessebe have.
http://www.biodiversityexplorer.org/mammals/ruminantia/damaliscus_lunatus.htm